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Low Ci (low + ci)
Selected AbstractsCYANOBACTERIAL ACCLIMATION TO RAPIDLY FLUCTUATING LIGHT IS CONSTRAINED BY INORGANIC CARBON STATUS,JOURNAL OF PHYCOLOGY, Issue 4 2005Tyler D. B. MacKenzie Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered depending on inorganic carbon (Ci) availability. Under steady light of 50 ,mol photons·m,2·s,1, the growth rate of Synechococcus elongatus PCC7942 was similar in cells grown in high Ci (4 mM) and low Ci (0.02 mM), with induced carbon concentrating mechanisms compensating for low Ci. Growth under fluctuating light of a 1-s period averaging 50 ,mol photons·m,2·s,1 caused a drop in growth rate of 28%±6% in high Ci cells and 38%±8% in low Ci cells. In high Ci cells under fluctuating light, the PSI/PSII ratio increased, the PSII absorption cross-section decreased, and the PSII turnover rate increased in a pattern similar to high-light acclimation. In low Ci cells under fluctuating light, the PSI/PSII ratio decreased, the PSII absorption cross-section decreased, and the PSII turnover remained slow. Electron transport rate was similar in high and low Ci cells but in both was lower under fluctuating than under steady light. After acclimation to a 1-s period fluctuating light, electron transport rate decreased under steady or long-period fluctuating light. We hypothesize that high Ci cells acclimated to exploit the bright phases of the fluctuating light, whereas low Ci cells enlarged their PSII pool to integrate the fluctuating light and dampen the variation of the electron flux into a rate-restricted Ci pool. Light response curves measured under steady light, widely used to predict photosynthetic rates, do not properly predict photosynthetic rates achieved under fluctuating light, and exploitation of fluctuating light is altered by Ci status. [source] INORGANIC CARBON REPLETION DISRUPTS PHOTOSYNTHETIC ACCLIMATION TO LOW TEMPERATURE IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS,JOURNAL OF PHYCOLOGY, Issue 2 2005Robert A. Burns Acclimation of cyanobacteria to ambient fluctuations in inorganic carbon (Ci) and temperature requires reorganization of the major protein complexes involved in photosynthesis. We grew cultures of the picoplanktonic cyanobacterium Synechococcus elongatus Naegeli across most of its range of tolerable temperatures from 23 to 35°C at both low (<0.1 mM) and high Ci (approximately 4 mM). Over that range of temperatures, the chl-based doubling time did not differ between low and high Ci grown cells but did increase with decreasing temperature. Cells grown at 23°C high Ci showed an elongated morphology, which was not present in 23°C low Ci cells nor at 35°C high and low Ci. Furthermore, 23°C high Ci cells showed premature senescence and death compared with all other treatments. Phycocyanin per cell was greater in high Ci grown cells at all temperatures but showed a characteristic decrease with decreasing temperature. Functional PSII determination showed that 23°C high Ci cells had 1.5 × 105 PSII·cell,1 compared with only 6.9 × 104 PSII·cell,1 for 23°C low Ci. The 35°C high and low Ci cells had 7.7 × 104 and 6.4 × 104 PSII·cell,1, respectively. These data were supported by immunoblot determinations of PsbA content·cell,1. As a result of their high PSII·cell,1, 23°C high Ci cells generated more reductant from PSII than could be accommodated by downstream assimilative metabolism, resulting in early senescence and death of 23°C high Ci cells, probably as a result of the generation of reactive byproducts of electron transport. [source] Naturally low carbonic anhydrase activity in C4 and C3 plants limits discrimination against C18OO during photosynthesisPLANT CELL & ENVIRONMENT, Issue 9 2000J. S. Gillon ABSTRACT The 18O content of CO2 is a powerful tracer of photosynthetic activity at the ecosystem and global scale. Due to oxygen exchange between CO2 and 18O-enriched leaf water and retrodiffusion of most of this CO2 back to the atmosphere, leaves effectively discriminate against 18O during photosynthesis. Discrimination against 18O (,18O) is expected to be lower in C4 plants because of low ci and hence low retrodiffusing CO2 flux. C4 plants also generally show lower levels of carbonic anhydrase (CA) activities than C3 plants. Low CA may limit the extent of 18O exchange and further reduce ,18O. We investigated CO2,H2O isotopic equilibrium in plants with naturally low CA activity, including two C4 (Zea mays, Sorghum bicolor) and one C3 (Phragmites australis) species. The results confirmed experimentally the occurrence of low ,18O in C4, as well as in some C3, plants. Variations in CA activity and in the extent of CO2,H2O isotopic equilibrium (,eq) estimated from on-line measurements of ,18O showed large range of 0,100% isotopic equilibrium (,eq= 0,1). This was consistent with direct estimates based on assays of CA activity and measurements of CO2 concentrations and residence times in the leaves. The results demonstrate the potential usefulness of ,18O as indicator of CA activity in vivo. Sensitivity tests indicated also that the impact of ,eq< 1 (incomplete isotopic equilibrium) on 18O of atmospheric CO2 can be similar for C3 and C4 plants and in both cases it increases with natural enrichment of 18O in leaf water. [source] | ||||||||||